1. Field of the Invention
The present invention relates to a holing sewing machine and in particular to such a holing sewing machine which includes a workpiece-presser elevating and lowering mechanism, a needle-thread cutting mechanism, a bobbin-thread cutting mechanism, and an interlocking mechanism which mechanically interlocks the above three mechanisms to one another.
2. Related Art Statement
A generally known holing sewing machine that forms holing stitches for, e.g., a button hole, includes a workpiece-presser elevating and lowering mechanism which elevates and lowers a workpiece presser; a needle-thread cutting mechanism which cuts a needle thread conveyed by a sewing needle; a bobbin-thread cutting mechanism which cuts a bobbin thread supplied from a bobbin; an interlocking mechanism which mechanically interlocks the above three mechanisms with one another; and a drive device which drives those three mechanisms via the interlocking mechanism. Thus, the holing sewing machine is constructed to be able to perform the cutting of the needle and bobbin threads and the elevating of the workpiece presser in a substantially continuous manner. A pedal-operated drive device is generally known as the above-indicated drive device. The pedal-operated drive device includes a foot pedal which is pushed by a foot of a user; and a chain member which drives the above three mechanism when the foot pedal is pushed by the user's foot.
FIG. 9 shows a generally known bobbin-thread cutting mechanism 100. A cam lever 102 is fixed to a right-hand end portion of a horizontal axis member 101 which is pivotally supported by a frame of a holing sewing machine. A roller member 103 which is attached to a rear end portion of the cam lever 102 is engaged with a cam groove 105 of a plate cam 104 which is supported by the machine frame such that the plate cam 104 is pivotable about a horizontal axis line. When a first operative lever 106 fixed to a left-hand end portion of the axis member 101 is pivoted in a direction indicated at an arrow by a chain member 119 being pulled by a foot pedal (not shown), the axis member 101 and the cam lever 102 are pivoted as a unit with the first operative lever 106. Since the roller member 103 is engaged with the cam groove 105, the plate cam 104 is pivoted in a direction indicated at an arrow.
A rear end portion of a bobbin-thread-cut link 110 is connected via a pin to the plate cam 104, and a rear end portion of a second operative lever 111 is connected to a front end portion of the bobbin-thread-cut link 110. A movable blade 112 and a bobbin-thread-draw member 113 are fixed to a front end portion of the second operative lever 111. When the plate cam 104 is pivoted in the direction indicated at the arrow, the bobbin-thread-cut link 110 is moved rearward, the movable blade 112 and the bobbin-thread-draw member 113 are pivoted as a unit with the second operative lever 111, about a stepped screw 114, in a direction indicated at an arrow.
When the movable blade 112 and the bobbin-thread-draw member 113 are pivoted in the direction indicated at the arrow, first, a predetermined amount or length of a bobbin thread is drawn from a bobbin (not shown) by the bobbin-thread-draw member 113, and then the movable blade 112 cooperates with a fixed blade 115 to cut the bobbin thread. The present bobbin-thread cutting mechanism 100 is mechanically interlocked with a workpiece-presser elevating and lowering mechanism and a needle-thread cutting mechanism (not shown) by an interlocking mechanism 118 including a link member 117. The chain member 119 and the foot pedal cooperate with each other to provide a pedal-operated drive device which drives the three mechanisms via the interlocking mechanism 118.
However, the known holing sewing machine including the above-described four mechanisms and drive device suffers from the problem that if the bobbin-thread cutting mechanism 100 is operated at a high speed by the pedal-operated drive device, the bobbin thread may be broken when the thread is drawn from the bobbin by the bobbin-thread-draw member 113 before being cut by the cooperation of the movable and fixed blades 112, 115. Thus, the bobbin-thread cutting mechanism 100 cannot be operated at so high speeds. In this sort of holing sewing machine, since the user needs to operate the foot pedal, he or she feels a great operation load. In addition, since the user needs to operate carefully the foot pedal for the bobbin-thread-draw member 113 so as not to brake the bobbin thread, the efficiency of operation of the sewing machine cannot be improved.
Recently, an air-operated cylinder device or a solenoid-operated actuator is used as a drive device for operating the above-indicated three mechanism. However, each of those actuators is operated such that the speed of operation of the each actuator is not changed.